Polymeric materials find use in many areas of consumer products and industrial design. Polymeric materials are formed from individual units of monomers. When a polymer is formed from monomers that are all the same it is called a homopolymer, when a polymer is formed from a mixture of more than one monomer it is known as a copolymer. The polymers can be formed from random mixtures of monomers or the order of monomer addition can be non-random. One form of polymer with non-random addition is known as a block copolymer. In a block copolymer the polymer is formed from blocks of different monomers. For example one block could be a sequence of all methyl methacrylate monomers and another block could be all methacrylate monomers. In other examples one block can be a random mixture of two or more monomers followed by a block formed from a single monomer; these are still known as block copolymers. Block copolymers are highly desired because of the unique properties that can be achieved in polymers formed as block copolymers.
A common method for forming polymers in general is through free radical polymerization. Free radical polymerization can be used to create random polymers; however, it is not useful for creating block copolymers. Instead of free radical polymerization living radical polymerization (LRP) or controlled radical polymerization (CRP) procedures have been utilized to create polymers since the 1990s. These procedures can be used to create block copolymers, two well-known forms of these procedures are the Atom Transfer Radical Polymerization (ATRP) and Reversible Addition/Fragmentation Chain Transfer (RAFT). For these procedures the size of the final copolymers is determined by the ratio of monomer to initiator. One advantage of LRP is that because of the way the process occurs the polydispersity of the resulting copolymer tends to be lower, meaning a more uniform copolymer size range. Since the reactions proceed until the monomers are used up the processes allow one to tailor the size of the copolymer. In addition, these processes can be used to create block copolymers. One problem that has been associated with these two processes is that the polymers formed using them tend to be dark or have coloration in the polymer. It is not known what these colors are due to; however, dark coloration is generally not desired especially when the polymers are incorporated into items like labels, tapes and adhesives. In addition, the dark or colored appearance can interfere with the cure of UV curable adhesives that these polymers find use in. Another disadvantage of these processes is that sometimes the required reaction temperatures are quite high and it would be desirable to be able run the polymerization reactions at lower temperatures.
Another form of LRP is the one used in the present disclosure, namely Single Electron Transfer-Living Radical Polymerization SET-LRP. One main difference from ATRP and RAFT is that in SET-LRP the catalyst is a solid, namely, copper wire or copper mesh. One other advantage is that generally the SET-LRP process can be run at lower temperatures.
It is desirable to provide a process that would allow for relatively rapid polymerization of block copolymers having a very narrow number average molecular weight (Mn) range and to a controlled size. It is also desirable to produce block copolymers that have a polydispersity index (weight average molecular weight/number average molecular weight) (Mw/Mn) ratio that is as close to 1 as possible. It is also desirable to provide a process that can be conducted at lower temperatures and that results in copolymers with low to no color and that include UV curable crosslinking functions in the copolymer. It is especially desirable to produce block copolymers that are UV crosslinkable and that can be utilized in hot-melt adhesive systems.